AU2006337481B2

AU2006337481B2 - Self-tapping and thread-forming screw

Info

Publication number: AU2006337481B2
Application number: AU2006337481A
Authority: AU
Inventors: Frank Langewiesche
Original assignee: Spax International GmbH and Co KG
Current assignee: Spax International GmbH and Co KG
Priority date: 2006-01-12
Filing date: 2006-10-20
Publication date: 2010-10-28
Anticipated expiration: 2026-10-20
Also published as: AU2006337481A1; US7677854B2; EP1971786B1; RU2382915C1; MX2008008836A; EP1971786A1; PL1971786T3; ATE451558T1; ES2336258T3; HRP20100041T2; DE202006000479U1; CA2636829A1; PT1971786E; SI1971786T1; US20070160440A1; DE502006005629D1; RS51160B; CN101360922A; DK1971786T3; WO2007087904A1

Abstract

The invention relates to a self-boring and thread-forming tapping screw having a screw shaft with a screw tip at one end and at the other end a force application member for the transmission of a turning moment. The screw shaft includes a threaded section with the screw tip and an adjacent thread-free section of the shaft including the force application member. The threaded section has a shaft core and a self-tapping thread. The threaded section includes a core section axially displaced from the tip and having a polygonal core cross section. Corners of the core cross section define an enveloping circle with an enveloping circle diameter larger than a shaft diameter of the thread-free section.

Description

11573/VII/bj ABC Verbindungstechnik GmbH & Co. KG, K6lner Str. 71-77, 58256 Ennepetal Self-tapping and thread-forming screw 5 The present invention relates to a self-tapping and thread-forming screw having at one end a screw shaft with a screw tip and at the other end a point of application of a force for the transmission of a 10 turning moment, the screw shaft consisting of a threaded section exhibiting the screw tip and an adjacent thread-free section of the shaft exhibiting the point of application of a force, the threaded section consisting of a shaft core and a thread 15 forming, single or multiple thread. Screws of this kind, which, because of their thread free section of the shaft, are also designated as part threaded screws, can also be screwed directly without 20 pre-drilling into relatively soft materials, such as wood and the like. It has been established in practice in conjunction with this that the thread-free section of the shaft generates high friction on entering the threaded hole formed by the threaded section, which 25 leads to a disadvantageously high driving moment. Previously disclosed in relation to a part-threaded screw of this kind is the provision of the thread-free section of the shaft in its area adjacent to the 30 threaded section with a so-called shaft cutter, which consists of radially projecting cutting ribs that are intended to enlarge the threaded hole during driving to such an extent that the section of the shaft is able to penetrate with reduced friction and consequently with a 35 reduced driving moment. Manufacture by a rolling process is problematical, however, in the case of such screws. Deformation of the screw by bending can occur in the area of the shaft cutter during rolling, This means that an exactly straight screw cannot be 11573/VII/bj - 2 produced, or can only be produced with an additional cost. The object of the present invention is to make 5 available a screw of the aforementioned kind, which, on the one hand, is capable of being driven with a low driving moment and, on the other hand, can be produced in a simple and economical manner with high accuracy (in particular, with exact straightness). 10 According to the invention, this is achieved in that the threaded section, in an area situated remotely from the screw tip, exhibits a core section having a polygonal core cross section, which with its corners 15 defines an enveloping circle with an enveloping circle diameter which is larger than the shaft diameter of the thread-free section of the shaft. The outcome of this is that the polygonal core section with its corners causes the threaded hole to expand during driving, with 20 the subsequent result that the friction and the driving moment are reduced as the thread-free section of the shaft penetrates. The arrangement of the polygonal core section in accordance with the invention in the area of the threaded section (and not approximately in the area 25 of the thread-free section of the shaft) produces the advantageous outcome in the production of the screw by a rolling process that the screw is guided exactly ("clamped") between the roller jaws over the thread, including directly in the area of the polygonal section 30 of the core, so that bending phenomena are excluded from the axis of the screw. The invention thus permits simple and rapid manufacture with high precision in the rolling process. 35 Additional advantageous characteristics of the invention are contained in the dependent claims and in the following description. The invention will now be described in more detail with 1 1573/VII/bj - 3 reference to two preferred illustrative embodiments depicted in the drawing, in which: Fig. 1 depicts a side view of a screw according to the 5 invention in a first, preferred embodiment; Fig. 2 depicts an enlarged cross section in the plane II-II according to Fig. 1; 10 Fig. 3 depicts a side view of a second embodiment of the screw according to the invention; and Fig. 4 depicts an enlarged cross section in the plane IV-IV according to Fig. 3. 15 A screw 1 according to the invention consists in both embodiments of a long and narrow screw shaft 2 having at one end a screw tip 4 and at the other end a point of application of a force 6 for the transmission of a 20 turning moment. In the depicted embodiments, the point of application of a force 6 is embodied as an internal point of application of a force and as such is not actually distinguishable in the side views. In addition, the point of application of a force 6 is 25 formed on or in a screw head 8, which is preferably executed as a countersunk head. The point of application of a force 6 can be formed as a cross-head, an internal hexagonal socket head, a hexalobular internal driving button head (TORX) or the like. It can 30 also be an external point of application of a force, for example an external hexagonal socket head. The screw shaft 2 consists of a threaded section 10 exhibiting the screw tip 4 and an adjacent, thread-free 35 section of the shaft 12 exhibiting the point of application of a force 6 and the screw head 8. The thread-free section of the shaft 12 exhibits a cylindrical peripheral surface with a shaft diameter DS. The threaded section 10 consists of a shaft core 14 1 1573/VII/bj - 4 and a thread-forming tapping thread 16, being a single thread in the case depicted here, in the form of a radial elevation running in the form of a helical line. With its external thread edge 18 formed between tw'o 5 flanks, the thread 16 defines an external thread diameter DG. According to the invention, the threaded section 10 exhibits a core section 20 with a polygonal core cross 10 section in an area remote from the screw tip 4. As can be appreciated in particular from the cross sections depicted in Figs 2 and 4, the polygonal core section 20 with its corners 22 defines an enveloping circle 24 with an enveloping circle diameter DH, which is larger 15 than the shaft diameter DS of the thread-free shaft section 12, although it is preferably smaller than the thread diameter DG. The enveloping circle diameter DH should preferably be up to 1.4 times, and in particular between 1.1 and 1.2 times the diameter of the shaft DS. 20 In an 8 mm screw, for example, the thread diameter DG is 8 mm, and the shaft diameter DS is about 5.6 mm. According to the invention, the enveloping circle diameter DH in this case lies in the range from about 6.2 mm to 6.4 mm, 25 In the first embodiment illustrated in Figs 1 and 2, the thread 16 runs along the entire core 14 of the shaft including the polygonal core section 20. In this way, the polygonal core section 20 can preferably be 30 arranged in the end area of the threaded section 10 on the shaft side (at the thread run-out) in direct proximity to the thread-free section 12 of the shaft. Exact straightness is nevertheless achieved in the manufacture of the screw 1 by the rolling process, in 35 that the area of the polygonal core section 20 is guided precisely, practically clamped, over the continuous thread 16 between two roller jaws. The thread 16 also passes with its outer thread edge 18 over the area of the polygonal core section 20 - viewed ll573/VII/bj - 5 in an axial projection - with a constant radius in the form of a circle (see Fig, 2). Unlike the embodiment depicted in Fig. 1, the polygonal core section 20 provided with a thread 16 can also be arranged in the 5 threaded section 10 at a greater distance from the thread-free section 12 of the shaft, in which case a part of the "normal" thread with a cylindrical shaft core 14 is provided between the sections 20 and 12. 10 In the alternative embodiment according to Figs 3 and 4, the polygonal core section 20 - interrupting the thread 16 - is of thread-free execution. An end area of the threaded section 10, preferably with at least one complete turn of the thread, is provided for this 15 purpose between the polygonal core section 20 and the thread-free section 12 of the shaft. According to Fig. 3, this may also involve at least four complete turns of the thread. A part of the threaded section 10 is thus situated axially to either side of the polygonal 20 core section 20, so that exact guiding to prevent distortion/bending is also achieved in this embodiment in conjunction with rolling the thread. In both embodiments, the polygonal core section 20 25 exhibits an axial length L, which corresponds more or less to the length of a part of the threaded section 10 having between one and six turns of the thread. As can be appreciated in addition from Figs 2 and 4, 30 the polygonal core cross section of the core section 20 is preferably embodied as a four-sided figure (square or quadrilateral). It is fundamentally possible, however, to choose a preferably equilateral, three sided to six-sided figure for this. The lateral 35 surfaces in this case, unlike in the depictions, can be curved in a weakly concave or convex manner. The corners 22 should be as square-edged as possible, although they can also be slightly rounded.

11573/VII/bj - 6 In a preferred embodiment of the invention, the screw tip 4 also exhibits a core 26 with a polygonal core cross section. The thread 16 in this case passes with its outer thread edge 18 - viewed in an axial 5 projection - over the area of the tapering screw tip 4 and as far as a pointed end 28 with a continuously reducing radius in the form of a spiral over the core 26. Provided in addition, preferably in conjunction with the tip 4 of the screw, is a transitional section 10 30, which exhibits a core 32 with a constant, similarly polygonal core cross section over its axial length. This core cross section corresponds in particular to the core cross section that is present in the directly adjacent area of the core 26 of the tip 4 of the screw. 15 The thread 16 passes over the azea of the core 32 of the transitional section 30 with its outer thread edge 18 - in this case, too, viewed in an axial projection in a similar manner to the rest of the threaded section 10 with a constant radius in the form of a circle. 20 In the case of the core cross sections of the core 26 of the screw tip 4 and the core 32 of the transitional section 30, it is preferably also a matter of a quadrilateral or a square, or any in particular 25 equilateral, three-sided to six-sided figure. The polygonal core 32 of the transitional section 30 with its corners defines an enveloping circle, the diameter of which, on the one hand, is larger than the diameter of the core 14 of the shaft, but, on the other hand, is 30 smaller than the enveloping circle diameter DH of the core section 20 according to the invention. By means of the preferred embodiment described here in the area of the tip 4 of the screw, this acts as a 35 boring tip, which permits centered and easy driving. The invention is not restricted to the illustrative embodiments depicted and described here, but also includes all embodiments of identical effect within the 11573/VII/bj - 7 scope of the invention. Moreover, the invention is also as yet not restricted to the combination of characteristic features defined in Claim 1, but can also be defined by any other desired combination of 5 particular characteristic features of all previously disclosed individual characteristic features. This means, fundamentally, that practically every individual characteristic feature in Claim 1 can be omitted, and can be replaced by at least one individual 10 characteristic feature disclosed elsewhere in the application. In this respect, Claim 1 is to be understood only as a first attempt at the formulation of an invention.

Claims

1. A self-boring and self-tapping screw comprising a screw shaft with a screw tip at one end extending axially to a force application member for the transmission of a 5 turning torque at the other end, the screw shaft including a threaded section disposed between the screw tip and a thread-free section of the shaft, the thread free section including the force application member, the threaded section including a shaft core and a thread, the threaded section further includes a core section axially displaced from the screw-tip, the core section has a polygonal core cross 10 section with corners defining an enveloping circle having an enveloping circle diameter larger than a shaft diameter of the thread-free section of the shaft; wherein the thread runs along the entire core, including the polygonal core section, and the polygonal core section is provided within the threaded section adjacent the thread-free section of the shaft. 15

2. The screw according to claim 1, wherein the enveloping circle diameter of the polygonal core section is equal to or less than 1.4 times the shaft diameter of the thread-free section of the shaft.

3. The screw according to claim 1, wherein the enveloping circle diameter of the polygonal core section is between 1.1 and 1.2 times the shaft diameter of the 20 thread-free section of the shaft.

4. The screw according to claim 1, wherein an outer thread edge defines a constant radius circle.

5. The screw according to claim 1, wherein the thread runs over the screw tip and an outer thread edge defines a continuously reducing radius spiral over the tip 25 core.

6. The screw according to claim 5, further including a transitional section adjacent the tip, the transitional section having a transitional core with a constant polygonal core cross section corresponding to the cross section of the tip core directly adjacent the transitional section of the screw, the thread passes over the area of 9 the transitional core of the transitional section with its outer thread edge forming a constant radius circle.

7. The screw according to claim 1, wherein the polygonal core section includes an axial length corresponding approximately a length of the threaded section having 5 between one and six turns of the thread.

8. The screw according to claim 1, wherein the polygonal core cross section comprises an equilateral polygon having three to six sides.

9. The screw according to claim 1, wherein the thread-free section of the shaft transitions into a countersunk screw head.